Major Peake is spending almost six-and-a-half hours outside the ISS as he and Nasa colleague Tim Kopra carry out repairs to a broken power unit.

The two are working in 45-minute blocks of daylight, then complete darkness, as the station orbits Earth every one-and-a-half hours.

Major Peake is the first “official” British astronaut to embark on a spacewalk. Michael Foale, who has dual UK/US citizenship, was the first Briton to do this, in 1995, but he was working under a US banner.

Major Peake and Colonel Kopra entered an airlock before opening a hatch and heading outside, where they are tethered to the ISS to ensure they do not drift off. They should finish the repairs in under three hours, and at that point ground control will perform some checks.

The six hours they will spend outside will be tiring because of the pressurised suits they are wearing. They also face the prospect of being temporarily blinded by sunrises and will need to regularly check one another to make sure their suits have not been damaged. They will be able to drink water from pouches, but will not have a toilet break.

‘Exhilarated’

Writing in his blog, Major Peake said he felt “exhilarated” by the prospect of walking in space, but said: “I have no time to dwell on these emotions. The six hours and 30 minutes we will work on the space station’s hull are meticulously planned and Tim and I need to execute each step methodically.”

Before the spacewalk began, British-born US astronaut Nicholas Patrick, a spacewalk veteran, said Major Peake should find time to enjoy the “majesty of the view” during his walk.

He told the BBC Radio 4 Today programme: “When you float out, it is a remarkable feeling. You are used to floating. By this point Tim has been in space for a month, he will know exactly what floating is like.

“What he won’t be used to is being outside the space station with a fabulous view and, perhaps more importantly, with a very difficult set of time-critical tasks ahead of him.

‘Wonderful experience’

“My bet is that, like me, when he goes out he won’t be looking down initially, he will be looking left and right, finding his way around and getting ready for the tasks ahead. But it’s a great thing to go out, it’s really a wonderful experience.”

There have been 191 spacewalks for maintenance at the space station, including a similar walk completed in 2014 by Nasa astronaut Reid Wiseman, who will help guide Major Peake and Colonel Kopra from mission control in Houston, Texas.

Major Peake, a former Army Air Corps and helicopter test pilot, is the first Briton aboard the ISS and the first fully professional British astronaut employed by a space agency.

Previous Britons in space have either had US or dual citizenship or been on privately funded or sponsored trips. Major Peake, who works for the European Space Agency, arrived at the ISS on 15 December 15 on a six-month mission.